RAAus magazine

[Moneybox]

The statement on exceeding Vne at high altitude is interesting. The article states due to the lower air density you could exceed Vne by TAS even thought the IAS is within limits however I'd argue that due to the lower air density the plane would not be likely to exceed it's structural design.

[spacesailor]

I always thought , the thinner the air ,

the VNA would be moot .

Look at the speed of satellites.  They certainly couldn't do that speed at  "mean sea level "  .

spacelsailor

 

[skippydiesel]

1 hour ago, Moneybox said:

I think the rest of the article from Page 80-83 explain it in detail. Quite a good informative read.

 

I actually picked up the previous magazine by mistake, still unopened, and found another interesting article on building your own airstrip.

Well I have been flying for a while now, very far from an expert, but I found it to be confusing and possibly even wrong in parts.

1 hour ago, Moneybox said:

 

 

It seemed relevant right now 😄 

Looks like you might be getting a good camber on it. Dont over do it. It may make landing on a wet surface/crosswinds, a tad more difficult than it needs to be.😈

[skippydiesel]

1 hour ago, Moneybox said:

The statement on exceeding Vne at high altitude is interesting. The article states due to the lower air density you could exceed Vne by TAS even thought the IAS is within limits however I'd argue that due to the lower air density the plane would not be likely to exceed it's structural design.

Your enturing into pretty expert territory here. 

Airspeed, as you climb,  will be a poor indication of true speed, due to the lower air pressure (ASI working off pressure differential). The higher you go above sea level, the greater the error.

 

In the past we used the rough estimate of 2% for every 1000 ft ASL. In a 100 knot aircraft, 2 knots error (ASI reading low)/1000 ft.

Now we have GPS systems that give an instant and likly accurate readout of True Air Speed.

 

I vaguely recall that at altitude, Vne can be easily exceeded by the unwary pilot - may have had something to do with air molecule's exciting the airframe (flutter?) -- where is that expert when needed?

 

So it seems to me that the pilot must go by  True airspeed and keep his aircraft below Vne as indicated by this system (not the ASI) 😈

[facthunter]

Back to Basics. GPS is not  true airspeed unless you Know the Wind velocity, your groundspeed and track and sum the vectors.  "Pilot Institute" will give you this stuff FREE..  .Nev.

Edited yesterday at 05:51 AM by facthunter
more content.

[kgwilson]

I finally got round to reading the article. Every pilot should know what all the airspeed terms are and what they mean as well as their relationship with one another. It is part of the training and qualification process. I think the authors presentation and sequencing could have been a lot better & he failed to mention calibrated airspeed at all which is the AS corrected for position installation errors but maybe that would just serve to confuse some even more.

[spacesailor]

" calibrated airspeed " .

CAS I thought meant computered air Speed .

spacesailor

[aro]

15 hours ago, skippydiesel said:

Now we have GPS systems that give an instant and likly accurate readout of True Air Speed.

 

I vaguely recall that at altitude, Vne can be easily exceeded by the unwary pilot - may have had something to do with air molecule's exciting the airframe (flutter?) -- where is that expert when needed?

 

So it seems to me that the pilot must go by  True airspeed and keep his aircraft below Vne as indicated by this system (not the ASI)

 

GPS is ground speed, so it is influenced by the wind and is not a measure of airspeed. With a low stall speed and strong wind, you can fly with GPS speed of zero.

 

TAS is the actual speed you are travelling through the air, i.e. the speed someone in a balloon floating with the wind with a radar gun would measure.

 

IAS is indicated airspeed, the speed that is shown on the airspeed indicator.

 

CAS is calibrated airspeed, which is what a perfect airspeed indication system would show. Airspeed indication systems are not perfect. IAS and CAS should be very close at cruise speed, but IAS often has large errors at high angle of attack, i.e. close to the stall.

 

IAS and CAS reduce approximately 2% per thousand feet due to reduced air density. Aerodynamic loads e.g. lift are relative to CAS so we can use indicated airspeeds for stall speed, approach speed etc.

 

Vne could be limited by aerodynamic loads, or it could be limited by flutter. Aerodynamic loads are related IAS(CAS) but flutter is relative to TAS.

 

Typically, small aircraft have a limited service ceiling, so if the ceiling is 14000 and VNE is 130 knots they might test for flutter to 190 TAS and just give the one number 130 IAS. If an aircraft has a higher ceiling e.g. gliders where altitude is not limited by the reducing engine power, VNE can be TAS or can change as altitude increases.

 

The biggest problem is e.g. experimental aircraft where people put a big engine in that allows it to go faster and higher. The spread between IAS and TAS can be bigger than was assumed when the Vne was set originally, so you can reach a higher TAS than it's designed for.

 

Summary:
Certified aircraft: Vne is whatever it says in the POH. Could be IAS, could be TAS or IAS changing with altitude.

Non-certified: There's no guarantee how Vne was tested. It is conservative to assume TAS, particularly if it has a larger engine than the original design.

[skippydiesel]

Hi Aro,

 

Very succinctly put - Thanks!

 

I should not have talked up GPS rather Dynon - my EFB gives me Air Speed, True Airspeed and Groundspeed.

In the not so distant past I only had airspeed and altitude, from which to estimate True. Groundspeed was based on time taken between ground points.😈

[facthunter]

Balloons don't have airspeed unless they have propulsion. Their groundspeed equals the winds speed/ Velocity Speed and direction.

   Your stall speed will stay the same (indicated) as you go higher but your actual speed  through the Air will increase approx 2 kts/1000 feet. Nev

[aro]

4 hours ago, facthunter said:

Balloons don't have airspeed unless they have propulsion. Their groundspeed equals the winds speed/ Velocity Speed and direction.

Right. Which is why if you measure the speed of an aeroplane with a radar gun from a balloon, you would get an accurate measurement of its true air speed (assuming the aircraft is travelling directly towards/away from the balloon)

[Red]

On 25/03/2025 at 3:20 AM, Moneybox said:

The statement on exceeding Vne at high altitude is interesting. The article states due to the lower air density you could exceed Vne by TAS even thought the IAS is within limits however I'd argue that due to the lower air density the plane would not be likely to exceed it's structural design.

This might help

                            https://flyingdonald.blogspot.com/2011/03/what-flutter.html